/* Copyright 2018 The OpenXLA Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#ifndef XLA_HLO_TRANSFORMS_DESPECIALIZER_H_
#define XLA_HLO_TRANSFORMS_DESPECIALIZER_H_

#include <iterator>
#include <utility>
#include <vector>

#include "absl/algorithm/container.h"
#include "absl/container/flat_hash_set.h"
#include "absl/status/statusor.h"
#include "absl/strings/string_view.h"
#include "xla/hlo/ir/hlo_casting_utils.h"
#include "xla/hlo/ir/hlo_instructions.h"
#include "xla/hlo/ir/hlo_module.h"
#include "xla/hlo/pass/hlo_pass_interface.h"
#include "xla/hlo/pass/hlo_pass_pipeline.h"

namespace xla {

// Creates an HloPassPipeline containing multiple HloPasses that can
// despecialize an optimized HloModule. This is useful to run an HloModule
// optimized for one specific platform on a different platform (undoing platform
// specific passes) with matching numerics for comparison.
//
// Current despecialization passes are HloDescheduler, ControlDepRemover,
// Defuser and BFloat16MixedPrecisionRemoval.
class Despecializer : public HloModulePass {
 public:
  Despecializer();
  void AddReduceWindowToReduceBroadcastDeconstruct();
  void AddAssumeGatherIndicesInBoundRewriteToCopy();
  absl::string_view name() const override { return "despecializer"; }

 protected:
  absl::StatusOr<bool> RunImpl(
      HloModule* module,
      const absl::flat_hash_set<absl::string_view>& execution_threads) override;

 private:
  HloPassPipeline pipeline_;
};

class AssumeGatherIndicesInBoundRewriteToCopy : public HloModulePass {
 public:
  AssumeGatherIndicesInBoundRewriteToCopy() = default;
  absl::string_view name() const override {
    return "AssumeGatherIndicesInBoundRewriteToCopy";
  }

 protected:
  absl::StatusOr<bool> RunImpl(
      HloModule* module,
      const absl::flat_hash_set<absl::string_view>& execution_threads) override;
};

class DeconstructReduceWindowToReduceBroadcast : public HloModulePass {
 public:
  DeconstructReduceWindowToReduceBroadcast() = default;
  absl::string_view name() const override {
    return "ReduceWindowToReduceAndBroadcast";
  }

 protected:
  absl::StatusOr<bool> RunImpl(
      HloModule* module,
      const absl::flat_hash_set<absl::string_view>& execution_threads) override;
};

// Pass which strips control dependencies from all instructions in the module.
class ControlDepRemover : public HloModulePass {
 public:
  ControlDepRemover() = default;
  absl::string_view name() const override { return "control-dep-remover"; }

 protected:
  absl::StatusOr<bool> RunImpl(HloModule* module,
                               const absl::flat_hash_set<absl::string_view>&
                                   execution_threads) override {
    bool changed = false;
    for (HloComputation* computation : module->computations()) {
      for (HloInstruction* instruction : computation->instructions()) {
        changed |= !instruction->control_predecessors().empty();
        TF_RETURN_IF_ERROR(instruction->DropAllControlDeps());
      }
    }
    return changed;
  }
};

}  // namespace xla

#endif  // XLA_HLO_TRANSFORMS_DESPECIALIZER_H_
